The present invention relates to a process for the safe treatment of radioactive sodium which was formed by the contamination with radioactive substances or by the radioactivation of liquid sodium used as sodium coolant for fast breeder reactors or in a fused fuel-liquid sodium interaction test.
Conventional methods for the treatment of sodium, regardless of whether it is radioactive or not, include (1) a method wherein sodium is heated to be reacted with water and oxygen in air by combustion, yielding Na.sub.2 O, Na.sub.2 O.sub.3, and NaOH; (2) a method wherein sodium is reacted with steam to form NaOH; (3) a method wherein sodium is reacted with an alcohol to form an alcoholate; and (4) a method wherein sodium is reacted with carbon dioxide gas or dry ice to form sodium carbonate. However, these methods have the following problems which must be solved in treating radioactive sodium. In method (1), fine smoke generated during combustion comprises radioactive sodium, the recovery or removal of which is very difficult. In method (2), the reaction must be conducted with great care. In method (3), large amounts of an alcohol is necessary because the solubility of sodium in the alcohol is small, and the waste alcohol must be disposed after the proper treatment. In method (4), large amounts of a gas must be treated and sodium must be strirred under heating to proceed the reaction because unreacted sodium is likely to remain in the central part of a reacting vessel.
The radioactivity of liquid sodium which was used in a fast breeder reactor and has reached a radioactive equilibrium is several m Ci/kg. Na. In the treatment of radioactive sodium having such radioactivity, particular attention should be given to the following points:
(a) The amount of the radioactive substances entrained with an exhaust gas to be released to external environments should be as small as possible.
(b) The reaction should be stable, controlled easily and securely, without a fear of explosion.
(c) The amount of wastes, e.g. waste liquor, discharged out of the facilities should be as small as possible.
(d) The process should be a simple one not necessitating so many secondary materials.
(e) The apparaus should be made compact.
(f) The radioactive corrosion materials entrained with the radioactive sodium should be simultaneously treated.
(g) From the viewpoint of the stability during temporary storage, the maintenance in the form of an alkaline or salt solution or of powder has a danger of leakage or scattering so that the radioactive substances should be maintained in a more stable form for example, as a vitrified body.